A high intake of zinc in supplements may raise the risk of prostate cancer, finds a recent study by a team at the US National Cancer Institute.
The researchers found that men taking more than 100mg of supplemental zinc daily were more than twice as likely to develop prostate cancer as men consuming less than this amount.
"Although we cannot rule out residual confounding by supplemental calcium intake or some unmeasured correlate of zinc supplement use, our findings, that chronic zinc oversupply may play a role in prostate carcinogenesis, warrant further investigation," wrote the authors in this month's issue of the Journal of the National Cancer Institute .
Zinc deficiency, associated with many diseases, including chronic liver disease, sickle cell disease and diabetes, is thought to affect around 2 billion people in the developing world, however in the US and Europe some people could be consuming too much of the nutrient in supplements. Nevertheless, the Health Food Manufacturers' Association in the UK recommends an upper safety level of 15mg zinc for daily self-supplementation while the EU Scientific Committee on Food suggests total daily intake should not exceed 25mg. Both of these are far from the 100mg levels tested by the researchers.
Using a 14-year follow-up trial, the Health Professionals Follow-Up Study, the researchers identified 434 cases of advanced cancer. Supplemental zinc, often taken to prevent or treat colds, at doses of up to 100 mg per day was not associated with prostate cancer risk but compared with nonusers, men who consumed more than 100 mg of supplemental zinc daily had a relative risk of advanced prostate cancer of 2.29. This increased to 2.37 for men adding zinc to their diet for 10 years or more.